INTERHEMISPHERIC FACILITATION OF THE HAND AREA OF THE HUMAN MOTOR CORTEX

We investigated interaction of the human bilateral hand motor area usi ng two magnetic stimulators. A conditioning shock over the motor corte x facilitated the response evoked in the ipsilateral first dorsal inte rosseous muscle by a test shock over the contralateral motor cortex gi ven under the limiting conditions of a small conditioning shock over a very small area and a small test shock. This effect was so weak that it was not elicited under slightly different conditions. We conclude t hat an excitatory, but weak, connection between strictly homotopic are as of the bilateral hand motor cortices exists in humans.